Electrical cords, and in particular extension cords, are used extensively in many applications, in both residential and commercial applications, because they provide a way to deliver electrical power from an electrical outlet to equipment that is far away from the outlet. However, there are significant issues surrounding safety and convenience that are associated with the use of extension cords.
One safety issue often associated with construction sites is the use of many extension cords because of the large number of tools that need electricity to operate. Typically these devices may not be plugged into the same cord because they would, in combination, require too much current to be safely provided through a single cord. This safety concern is especially true at construction sites where at least some of the equipment draws a large amount of power.
Furthermore, additional extension cords may be necessary because different pieces of equipment require different amounts of voltage to operate. For example, most electrically operated devices require a 120V source. However, some devices use a large amount of power and thus require 208V or 240V supplies.
Extensive usage of extension cords increases the probability of an electrical fault, cord degradation, or cord overloading. Cord degradation and failure when using a high-amperage power source and cord can cause fires, electrical shocks, and other hazards. Existing safety fuses and ground fault interrupter (GFI) circuits within electrical cords can sense sudden catastrophic electrical events, such as power failures, power surges, or other electrical or physical events caused on the source side of the electrical cord. These safety devices are integrated into the electrical cord and allow an electrical cord to disconnect upon occurrence of an electrical event.
Fuses and GFI circuits may not protect against various types of gradual failures, such as due to physical wear or thermal degradation. Sudden short circuits at the load end of the cord remain unprotected by these devices as well. Additionally, fuses and GFI circuits are typically connected in series with the cord so that if the fuse or GFI circuit is tripped, the entire cord is disabled. When a cord has multiple receptacles providing power to different tools and devices, a failure in one of the devices would trip the fuse or GFI and disconnect power to all of the receptacles and all of the devices that are plugged into the cord. Such an event can be startling and potentially hazardous to other users.
Heating is another safety problem for both commercial and residential extension cords even when the cord is overloaded. Extension cords that have a flaw such as a loose connector, partially broken wire, or kink have a point of increased resistance that causes resistive heating even when the current drawn through the cord is within its rated capacity. Such conditions can cause the extension cord to overheat and potentially ignite starting a fire, especially if the extension cord is adjacent a flammable material such as wood, clothing, or chemicals.
Yet another problem relates to extension cords that include locking mechanisms holding the male electrical plug portion in a female socket. These extension cords, called “twist lock” cords, prevent disconnection of the cord in case someone trips on the cord or the cord is otherwise unintentionally pulled from its socket connection to a power source, such as an electrical generator or a wall socket. When connecting a twist lock plug, the user inserts the plug into the receptacle and twists it to lock it in place to prevent it from being accidentally pulled from the receptacle. The difficulty is that the cross-section of the housing for a male twist lock plug is typically circular. Such configurations make it difficult to make a visual determination of whether the plug was properly twisted to lock it into the receptacle.
Additionally, construction workers and even casual residential users occasionally need to set up temporary power distribution for tools and use temporary lights to illuminate a room, work area, or work product. In some applications, the workers simply lay out a bunch of extension cords on the ground, which is dangerous because they are tripping hazards that the workers can fall over. The cords are also easily disconnected from one another and from their tools causing an unexpected loss of power. For lighting, the workers either plug in temporary lamps that rest on the floor, a table top, or create a temporary string of lights by hard wiring sockets to a pair of wires and hanging them from a ceiling or other structure. However, having to build a dedicated, hard wired light string is expensive and cumbersome.